Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 151751

Area Forecast Discussion
National Weather Service Des Moines IA
1151 AM CST Mon Jan 15 2018

.SHORT TERM.../Today through Tonight/
Issued at 308 AM CST Mon Jan 15 2018

Confidence: Medium to High

Main concern this period remains the cold and wind. Main thrust of
wind has already moved through immediately following the Arctic
front this evening.  From here out through 12z Tuesday...pretty
steady northwest winds of 15 to 25 mph with higher gusts expected.
This trend will gradually relax a bit from 06-12z Tuesday...but with
concurrent colder air moving into the region...headlines for extreme
cold remain warranted north with advisories across the remainder of
the south through 18z Tuesday as well. Patchy blowing snow or areas
of blowing snow will occur at ground level today and somewhat
tonight. This will have some impacts to travel...namely blowing some
of the loose snow back onto roadways and interstates.  Tire wipes
may lead to some compaction and possibly some slick spots here/there
so area motorists should be made aware of that potential today. We
may issue an SPS toward daybreak highlighting the potential but no
headlines other than cold planned for today.  Though some drier air
is being pulled in behind the vort max that brought the more
concentrated area of snowfall to central Iowa...upstream moisture
over Wisconsin/Minnesota continues to fill in around the deep upper
level trough which will rotate and expand back to the west overnight
tonight and Tuesday. This has some implications for cloud cover and
potential for light snow/flurries after sunset tonight. A lobe of
vorticity should accompany the rotation of the upper level low. With
some saturation in the dendritic layer at most locations after 00z
tonight through Tuesday have added scattered flurries or light snow
to areas northeast through south later today and tonight. Tonight`s
cloud cover will add some uncertainty to overnight low temperatures
and may keep readings a few degrees warmer.  Overall this should not
have much affect on expected wind chill values with winds remaining
brisk.  The bottom line is that H850 temperatures aloft will still
range from 20 to 26 below across the area (coldest west) by 00z this
evening then some moderation aloft overnight...but thickness still
about 504dm over the entire region at 12z Tuesday.  This will still
blanket the entire area with 20 to near 30 below wind chill values
in the advisory area...and 30 to 35 below readings in the warning
area for much of the period.

.LONG TERM.../Tuesday through Sunday/
Issued at 308 AM CST Mon Jan 15 2018

./Tuesday through Sunday/...Confidence Medium

We continue with cold morning wind chills across the region which
improve between 17 and 18z Tuesday.  Clouds will be on the decrease
during the afternoon as the upper level system and coldest air
begins to swing east/southeast. Light winds are anticipated during
the afternoon and evening hours which will improve conditions
outside. The main highlight for much of the remainder of the week
will be a building ridge over the western US with warming heights
and temperatures.  There has been some incredibly warm air in
western Canada (relatively speaking) at H850 due to downslope along
the Canadian Rockies.  This pocket of +10C air will be migrating
southeast and expanding/cooling a bit as it reaches the northern
Plains. However continued adiabatic warming in the lee of the
Rockies will intensify the warming with a gradual shift toward H850
temperatures warming to 10 to 15C from Iowa southwest into Oklahoma
by 18z Friday.  For us...warming.  Little sensible weather is
anticipated each day from Wednesday through Friday along with warmer
temperatures.  The main challenge may be melting...some overnight
fog and refreeze issues on roadways as the transition occurs.
Afternoon highs will recover from the single digits tomorrow to the
30s Thursday to 30s/40s Friday through Saturday. Looking ahead to
the weekend...a stronger signal of agreement between the GFS/Euro
for an advertised winter storm system cutting across Iowa and the
Northern Plains/Great Lakes.  A deepening trough is expected to
develop over the southwest/Southern Plains by 06z Sunday and eject
northeast Sunday.  There appear to be the usual timing differences
with the GFS about 6 hours faster right now and some differences
between models regarding track...though reasonably close at 7 days
out.  Given the origin of the storm in proximity of the Gulf states
this one should provide the region with some pretty decent
precipitation in the form of rain/snow or snow. Both the GFS/Euro
hint at the greater deformation precipitation to be across northwest
Iowa to northern Wisconsin.  Lot of details to resolve in the coming
days and definitely will be more to pass along through the mid to
end of the week.


.AVIATION.../For the 18Z TAFS through 18Z Tuesday afternoon/
Issued at 1151 AM CST Mon Jan 15 2018

VSBYS still reduced at many TAF sites this afternoon due to strong
gusty winds and blowing snow. Some light snow also possible into
this evening across the northeastern sites as the upper trough
moves overhead. Otherwise winds to slowly diminish tonight into
early Tuesday with low stratus remaining or building back in.


Wind Chill Advisory until noon CST Tuesday for IAZ027-028-038-

Wind Chill Warning until noon CST Tuesday for IAZ004>007-015>017-

Wind Chill Advisory from 3 PM this afternoon to noon CST Tuesday
for IAZ092>097.



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